1. Field of the invention:
The present invention relates to a magnetic core for speaker and, more particularly, to a compact magnetic core, which greatly reduces the weight of the speaker.
2. Description of the Related Art:
A variety of speakers have been disclosed for use in home stereo systems, audio/video systems, car stereo systems, etc., for voice output. A speaker has a magnetic core for producing lines of magnetic force or a magnetic loop. FIGS. 1 and 2 show a magnetic core for speaker according to the prior art. According to this design, the magnetic core comprises a magnetically conducting holder base B, a magnetically conducting center rod D vertically mounted on the top center of the holder base B, an annular magnet A mounted on the holder base B around the magnetically conducting center rod D, and a magnetically conducting annular plate C covered on the top side of the annular magnet A around the magnetically conducting center rod D. If the polarity of the magnetically conducting annular plate C is N pole, the polarity of the magnetically conducting center rod D becomes S pole, thereby causing a magnetic loop E to be produced.
FIG. 3 shows another structure of magnetic core for speaker according to the prior art. According to this design, the magnetic core comprises a hollow magnetically conducting hollow holder base G, a magnet F mounted in the hollow magnetically conducting hollow holder base G, and a magnetically conducting plate H covered on the topmost edge of the magnet F. When the annular top of the magnetically conducting hollow holder base G produced N pole, the magnetically conducting plate H produces S pole, resulting in a magnetic loop J around the magnetically conducting plate H within the magnetic holder base G.
The aforesaid two prior art designs have the common drawback of heavy weight. Because of the use of the magnetically conducting holder base B or G, the heavy weight of the magnetic core is unfavorable to portable speakers.
The present invention has been accomplished under the circumstances in view. It is therefore the main object of the present invention to provide a magnetic core for speaker, which is compact and lightweight. To achieve this and other objects of the present invention, the magnetic core comprises an annular magnet connectable to the body of the speaker, a center magnet mounted in the center of the annular magnet and connectable to the body of the speaker, an annular magnetically conducting plate mounted on the topmost edge of the annular magnet, and a center magnetically conducting plate mounted on the topmost edge of the center magnet for producing a magnetic loop with the annular magnetically conducting plate. Further, the annular magnet, the center magnet, the annular magnetically conducting plate and the center magnetically conducting plate commonly have a circular outer diameter. When installed, the annular magnet, the center magnet, the annular magnetically conducting plate and the center magnetically conducting plate are concentric.